It is known in the oil production industry to bring oil from underground formations to the surface using a rotary pump located downhole in the oil bearing formation and driven by a rotating rod string extending from a drive mechanism on the surface down through the well casing to the pump. Reciprocating pumps are also known where the rod string moved up and down by the drive instead of rotating.
Generally a polish rod clamp is clamped to a polish rod and a rotating or reciprocating drive is connected to the polish rod clamp such that the drive drives the polish rod clamp and thus the polish rod. The polish rod is essentially the top end of the rod string extending down to the pump such that driving the polish rod drives the pump.
Rotary drive mechanisms are disclosed for example in U.S. Pat. No. 6,241,016 to Dedels and U.S. Pat. No.4,716,961 to Makins, Jr. et al. The conventional polish rod clamp as illustrated in the mechanisms of Dedels and Makins. Jr. et al. typically comprises a pair of clamping members that clamp together by bolts extending lateral to the polish rod to clamp the polish rod between the clamping members.
U.S. Pat. No. 4,372,379 to Kulhanek et al. discloses a rotary drive mechanism supported above a well casing on a frame. The polish rod extends vertically upward through the middle of a rotating drive member and then a conventional rectangular polish rod clamp is clamped to the polish rod above the drive member. The bottom end of the polish rod clamp is engaged in the top of the drive member such that rotating the drive member rotates the polish rod clamp, the polish rod, the rod string, and the downhole pump. The weight of the rod string is supported on the drive member and frame.
Depending upon the length of the rod string from the surface to the pump, and the diameter of the rod string, and like factors with a rotary drive the top end of the rod string will typically rotate many times before the bottom end of the rod string, and thus the pump, begins to rotate. Rotary tension or torsion is thus present in the rod string during use. After stopping the rotary drive for service or like reasons, this torsion may be released by reversing the drive, or controlled by a brake or the like, however it is difficult to ensure that there is no torsion force being exerted between the polish rod and the drive through the polish rod damp. Releasing the clamping bolts on the polish rod thus can be hazardous.